I think that you can pump as many times per day as you want. the best way to tell if you are overworking your unit is by gauging EQ and, of course, general soreness. The only other thing that you want to watch out for with pumping is fluid retention, but I feel this is more about making sure you have good circulation, which means breaking up a session into shorter sets. I'm no vet, but I air-pump at pretty high pressures (sometimes as high as 12.5 inHg), but my temporary enlargements after each pump are 99% increased blood capacity. I accomplish this by doing 5 minute sets, then coming out of the pump and jelqing. everyone is different, so a little experimentation is your best bet to maximize your gains.
